Field of the Invention
The embodiments of the invention relate to an organic light emitting diode (OLED) display device, and more particularly, to an organic light emitting diode having improved emission efficiency and an OLED display device including the same.
Description of the Related Art
An OLED display device of new flat panel display devices has high brightness and low driving voltage. The OLED display device is a self-emitting type and has excellent characteristics of a view angle, a contrast ratio, a response time, a thin profile and so on.
In addition, there is a big advantage in a production cost. A fabricating process of the OLED display device is very simple and requires a deposition apparatus and an encapsulating apparatus.
The OLED display device includes an organic light emitting diode for emitting light. The OLED display device uses the light from the organic light emitting diode to display images.
FIG. 1 is a schematic cross-sectional view of a related art organic light emitting diode.
As shown in FIG. 1, the organic light emitting diode “D” includes a first electrode 10 as an anode, a second electrode 30 as a cathode and an organic emitting layer 20 therebetween.
The first electrode 10 as the anode is formed of a material having a higher work function than a material of the second electrode 30 as the cathode. For example, the first electrode 10 may be formed of one of indium-tin-oxide (ITO), and the second electrode 30 may be formed of aluminum (Al) or Al alloy (AlNd). The organic emitting layer 20 includes red, green and blue emitting patterns.
To increase emission efficiency, the organic material layer 20 may have a multi-layered structure. For example, the organic material layer 200 may include a hole injecting layer (HIL) 21, a hole transporting layer (HTL) 22, the emitting material layer (EML) 23, the electron transporting layer (ETL) 24 and the electron injecting layer (EIL) 25 sequentially staked on the first electrode 10.
In the organic light emitting diode “D”, the holes and the electrons respectively from the first and second electrodes 10 and 20 are combined in the EML 23 such that excitons are generated. When the electric energy of the exciton is changed into the light energy, the light having a color in accordance with an energy band gap of the EML 23 is emitted. According to the material of the EML 23, red, green and blue organic light emitting diodes are provided.
Recently, the phosphorescent material in place of the fluorescent material is increasingly used for a material of the EML. The singlet exciton generates a fluorescent type emission, while the triplet exciton generates a phosphorescent type emission. The singlet exciton has a formation probability of about 25%, while the triplet exciton has a formation probability of about 75%. Accordingly, the phosphorescent type emission has emission efficiency greater than the fluorescent type emission.
Since the emission efficiency of the organic light emitting diode “D” has a direct effect on the power consumption of the OLED display device, an increase in the emission efficiency of the organic light emitting diode “D” is a requirement. For example, new material used for the EML and having high emission efficiency may be developed for such an increase, or new material having high hole injecting or transporting property may be developed for such an increase.
However, there are still limitations to increasing the emission efficiency of the organic light emitting diode.